A modern model for the reception of broadcast radio that has traditionally been provided on the AM and FM bands is the satellite radio broadcast model now becoming popular in stationary locations, such as buildings, and on mobile locations, primarily automobiles at the present time. The general model for satellite radio broadcast is to broadcast radio signals from a satellite directly to a receiver. In some cases, particularly in dense urban areas, the satellite transmission may also be supplemented by ground transmitted signals.
In the United States, the FCC has allocated a spectrum in the “S” band (2.3 GHz) for nationwide broadcasting of satellite-based digital audio radio service (DARS). Sirius Satellite Radio and XM Satellite Radio have licenses in this band and provide DARS via satellite broadcast. Outside of the United States, the “L” band has been designated for use and WorldSpace uses the “L” band to broadcast in Europe, Africa and Asia, and in South America.
XM Radio uses two satellites in parallel geostationary orbits, one at 85 degrees west longitude and the other at 115 degrees west longitude. Radio receivers are programmed to receive and unscramble the digital data signal, which contains many channels of digital audio. In addition to the encoded sound, the signal contains additional information about the broadcast. The song title, artist and genre of music are all displayed on the radio. Sirius uses three satellites that form an inclined elliptical satellite constellation. WorldSpace, like XM uses geostationary satellites and provides DARS in the 1,467- to 1,492-megahertz (MHz) segment of the L-Band spectrum.
Energy traveling from satellites experiences a very large amount of attenuation. The power flux density incident at an antenna on an automobile, for example, may be on the order of 10−14 watts per square meter. Even in car installations, providing antenna systems has been difficult because the antennas must blend in with the automobile from an aesthetic point of view to be acceptable to consumers. In addition, the car provides blocking and attenuation effects that must be overcome.
A very desirable way to receive DARS from satellites would be on a truly portable unit, one that can be worn on the body of a person. The body unit presents antenna problems that are even more difficult to address, as antennas typically used for satellite reception in other applications (e.g., automobiles) to receive circularly polarized S and L band satellite broadcasts are not well suited to be worn on the body, and the body itself provides blocking effects.